Shori is a human who is capable of 'Polymorphing', which allows her to morph into multiple forms. Her alternate forms differ from regular enemies in that she can respawn a short time after her defeat. As a character, she has a rather important role in Tirahnys's history, having named it's various towns and cities. However, her greed had corrupted her and so she remains an earthbound spirit.
She serves as the game's secret boss, along with Sycor II and. Her battle has multiple phases: Phase 1 has her fight as herself, though she goes down easily. After that, Phase 2 has her morph into a fish (similar to Micren) with the battle taking place in a blue room with instakill spikes on the bottom. When that form goes down, she morphs into a green elephant with a square eye. Her next form is actually multiple Igors in a room with moving buzzsaws. Her true form is actually a green mushroom, which can charge at Serenity. Once that form is defeated, Shori dies and is no longer an earthbound spirt.
[Phase 1: Shori]
Machine Gun (A sound cue plays before firing off several rapid fire bullets.)
[Phase 2: Micren Shori]
Call Fish/Urchin (Calls upon fish and urchin, which can be shot for hearts)
Dark Shot (Fires several energy shots, which can be easily dodged)
[Phase 3: Elephant Shori]
Charge (Runs around, charging at anything in the way.)
[Phase 4: Igors]
Energy Machine Gun
[Phase 5: Ma Pignon]
Mini Copies (Copies of Shori drop from the ceiling, which can be killed for ammo and hearts.)
Love Coloured Master Spark[Touhou] Plays during the battle with Shori's first form.
Battle on the Big Bridge [FInal Fantasy V] Plays during the battles with Shori's polymorphed forms.
Chapter X of The Guardian Beasts shows that she had a hand in it's creation if her insistence of being called 'The Shapeshiftress' is anything to go by.
Despite how tough fighting multiple Igors would be, Serenity can go right and hide inside one of the lava pits, allowing her to easily dispatch them without taking damage from their attacks.
The room in the final phase appears to be bugged, because the player cannot move to the other side of the room due to an invisible wall.
Shori's true form is one of the few bosses in the game that cannot be damaged with Misery's End.